bridge: Add master device name to bridge fdb show

This patch adds master dev name from NDA_MASTER netlink attribute
 to bridge fdb show output

current iproute2 tries to print 'master' in the output if NTF_MASTER
is present. But, kernel today does not set NTF_MASTER during dump
requests. Which means I have not seen iproute2 bridge cmd print 'master' atall.
This patch overrides the NTF_MASTER flag if NDA_MASTER attribute is present.

Example output:

before this patch:
# bridge fdb show
44:38:39:00:27:ba dev bond2.2003 permanent
44:38:39:00:27:bb dev bond4.2003 permanent
44:38:39:00:27:bc dev bond2.2004 permanent

After this patch:
# bridge fdb show
44:38:39:00:27:ba dev bond2.2003 master br-2003 permanent
44:38:39:00:27:bb dev bond4.2003 master br-2003 permanent
44:38:39:00:27:bc dev bond2.2004 master br-2004 permanent

For comparision with the above, below is the output for NTF_SELF today,
# bridge fdb show
33:33:00:00:00:01 dev eth0 self permanent
01:00:5e:00:00:01 dev eth0 self permanent
33:33:ff:00:01:cc dev eth0 self permanent

If change in output is a concern, 'master' can be put at the end of the fdb
output line or made optional with -d[etails] option.

change from v1 to v2:
    use 'bridge' instead of 'master' in fdb show output

change from v2 to v3:
    use 'master' instead of 'bridge' in fdb show output
    (master could also be a vxlan device)
Signed-off-by: Wilson Kok <wkok@cumulusnetworks.com>
Signed-off-by: Roopa Prabhu <roopa@cumulusnetworks.com>

bridge/fdb.c

@@ -147,7 +147,10 @@ int print_fdb(const struct sockaddr_nl *who, struct nlmsghdr *n, void *arg)
 	}
 	if (r->ndm_flags & NTF_SELF)
 		fprintf(fp, "self ");
-	if (r->ndm_flags & NTF_MASTER)
+	if (tb[NDA_MASTER])
+		fprintf(fp, "master %s ",
+			ll_index_to_name(rta_getattr_u32(tb[NDA_MASTER])));
+	else if (r->ndm_flags & NTF_MASTER)
 		fprintf(fp, "master ");
 	if (r->ndm_flags & NTF_ROUTER)
 		fprintf(fp, "router ");